It is known, for example, from EP-A-0-997-676 or from U.S. Pat. No. 4,940,207, to produce a valve whose needle is actuated by magnetic coupling through a sealed partition, which enables the product passing through the valve to be separated physically from the control means without using a seal susceptible to degradation, in particular owing to wear by abrasion and/or corrosion. In known valves, the needle is equipped with permanent magnets which are to cooperate with permanent magnets carried by an actuating device in order together to constitute magnetic coupling means. The mounting of permanent magnets on the needle is a tricky operation which requires particular care of a kind which substantially increases the cost price of such a valve. The manufacturing and fitting tolerances of permanent magnets are such that the air gap between the needle and the associated actuating device must be relatively large in order to avoid frictional forces incompatible with the correct operation of the valve. This large air gap reduces the efficiency of the magnetic coupling sought. In addition, the magnets mounted on the needle are susceptible to attack by the fluid passing through the valve, and hence there is a risk of deterioration by abrasion and/or corrosion which may result in a decrease in the performance of such a valve.
It is those disadvantages which the invention more particularly aims to remedy by proposing a magnetic valve which is more economical and more reliable than the known valves, while its operation is entirely dependable.